Thermal recording method

ABSTRACT

A thermal recording is effected by applying a thermal pattern to a recording member having a recording layer composed of at least a polymer complex to produce a reversible latent image capable of being visualized.

United States Patent 1 1 1111 3,912,844

Endo et al. 1451 0a. 14, 11975 [54] THERMAL RECORDING METHOD 3,679,410 7/1972 Yrancken et al. 117/367 x ['75] Inventors: lchiro Endo, Kawasaki; Hiroshi r g gfg fi 'Q Kflkado, 3,764,335 10/1973 Nelson ll7/36.8 x

0 yo; 11c none, 0 yo; Kat'suhiko Nishide, Yokohama; OTHER PUBLICATIONS Kikuo Kinjo, Tokyo, a" f Japan SPSE 2nd Symposium on Unconventional Photographic Systems, 1967, pp. 49, 50, 137-139. Asslgneel Canon Kabushlkl Kalsha, Tokyo P. M. Cassiers: Photogr. Soci. & Eng., 4, pp. 199-202,

Japan (1960). 9 [22] Filed: June 1, 1973 Primary Examiner-Thomas J. Herbert, Jr. [2]] Appl' 366,010 Attorney, Agent, or Firm-Fitzpatrick, Cella, Harper & Scinto [52] US. Cl 428/500; 96/115 R; 427/145 51 Int. c1. B41M 5/18 ABSTRACT [58] Field of Search l 17/36.7, 36.8; 96/1 15 R; A thermal recording is efi'ected by applying a thermal 346/1 pattern to a recording member having a recording layer composed of at least a polymer complex to pro- [56] References Cited duce a reversible latent image capable of being visual- UNITED STATES PATENTS ized- 3,476,937 ll 1969 Vrancken ll7/36.l X 23 Claims, 3 Drawing Figures THERMAL RECORDING METHOD BACKGROUND OF THE INVENTION method comprising applying heat in the form of an image pattern (hereinafter called thermal pattern") to a heat sensitive material sheet such as a thennal recording sheet, and converting the resulting image to a visible image.

2. Description of the Prior Art Heretofore, there have been known many methods for converting a thermal pattern to a useful recording image such as a visible image or printing image. These methods are described in detail in lnsha Kogaku" ll, Shingo Henkanron, Chapter 5, Thermal Method, pp. 234-240, edited by Masanobu Wada, published by Kyoritsu Shuppan (1969), in which is described the conversion of a chemical, physical, electrical or magnetic change caused by heat on a recording sheet directly or indirectly to a visible image. Some of them will be explained below somewhat more in detail. There is used a thermal recording sheet produced by coating onto a substrate finely divided particles of a hydrophobic high polymer having a glass transition point of less than 40C such as polyethylene latex dispersed in a hydrophilic high polymer such as gelatin, casein, polyvinyl alcohol (PVA) andthe like. A thermal pattern is applied to this sheet to cause fusing of the hydrophobic resin particles at a high temperature portion resulting in change of various properties of the sheet surface such as mechanical strength, solubility, dye acceptability, inking property and the like. It is also possible to produce relief images or dye images by washing with water or soaking in an aqueous solution of dye after applying a thermal pattern or to use directly an offset printing plate. The above mentioned thermal recording methods and thermal recording sheets used therefor are disclosed in M. N. Vrancken: SPBE 2nd Symposium on Unconventional Photographic Systems (1967) and Japanese Patent Publication No. 1743/ 1964.

There are commercially available products produced according to. the above methods. For example, a polyester sheet covered with a hydrophobic resin emulsion and a pigment dispersed in an aqueous resin is exposed to a thermal pattern and washed with water wherein the portion subjected to high temperature to form a pigment image.

Also known is a thermal recording sheet capable of producing a visible image only by applying a thermal pattern without a developing treatment. Usually, such thermal recording sheets have a thermal recording layer composed of at least two kinds of solid reaction components capable of releasing active components as the result of melting or decomposing at a temperature corresponding to a high temperature portion of the thermal pattern,dispersed in a binder resin, and capable of producing a colored matter by reaction when heated. These reaction components are physically separated so that no reaction occurs at room temperature. However, when one of them is heated to the melting point or decomposition temperature, there is caused contact between both of them or the released active components to initiate the reaction and produce a colored matter. There have been known many kinds of reaction components and combinations thereof. A Representative one is a combination of a long chain fatty acid metal salt with a chelating agent or an organic reducing agent. Representative chelating agents are tannic acid, pyrogallol and spiropyrans, and a representative reducing agent is hydroquinone. As the result of mutual reaction, there is formed a visible image composed of metal chelate or metal.

The above-mentioned prior arts have many drawbacks. The image is composed of a pigment, metal chelate, metal and the like so that it is not possible to ob tain transparency, light color and high purity. These drawbacks are disadvantageous especially when the thermal recording sheet is used for a overhead projector or regeneration of color by a thermal recording method.

On the other hand, there is a drawback common among thermal recording sheets for converting a physical or chemical change caused by a thermal pattern to a visible image. This common drawback is that the production of the thermal recording sheet is carried out at a temperature lower than the heat response temperature (heat sensitive temperature) of the sheet. The heat sensitive temperature is a temperature which is sufficient to produce a visible image and generally ranges from C to 150C, preferably from C to C. For example, when a thermal recording sheet having a heat sensitive temperature of 80C is produced, the coating and drying should be naturally carried out at 15 60C for safety. In general the heat sensitive temperature when wetted with a solvent is lower than that of the dried coating so that it is more necessary to oper ate at low temperatures. The above difficulty is mainly due to irreversibility of response of the thermal recording sheet to heat or thermal response. There are known thermal recording methods and sheets having reversible thermal response. For example, a dielectric high polymer film is uniformly charged and then exposed to a thermal pattern. There occurs a rapid lowering of electric resistance at a temperature higher than the secondary transition temperature of the high polymer film and the electrostatic charge is decayed at a high temperature portion of the thermal pattern to produce an electrostatic pattern, which is then developed with a charged toner to produce a visible image. This method is published in P. M. Cassiers: Photogr', Sci, & Eng, 4, p. 199 1960) and is called electrothermography. Most electrothermography or other thermal recording sheets utilizing electric and magnetic changes which show reversible thermal response and therefore such difficulty as mentioned above is not present and high temperature coating is also possible. However these thermal recording methods need an additional operation such as charging, magnetization and the like and therefore the apparatus is disadvantageously complicated. The above-mentioned drawbacks are the cause of the high cost of commercially available thermal recording sheets.

The present inventors have now found that a thin film composed of a certain kind of high polymer complex shows a peculiar thermal behavier. This thin film is uniform and transparent and can not be dyed with a dye liquid developer at room temperature, but when heated at a temperature higher than a certain temperature, it can accept a dye from the dye liquid developer and be dyed. This property can be directly used for production of the thermal recording sheet and the thermal recording method. The high polymer complex thin film prosuch acceptability. in other words the heat response of the thermal recording sheet according to the present invention is reversible. The image portion capable of accepting a dye when exposed to a high temperature is hereinafter called a latent image in the present invention. It has also now been found that the latent image and other portions of the sheet exhibit differences in solubility and differences in gas permeability as well dye acceptability.

SUMMARY OF THE INVENTION An object of this invention is to provide a novel thermal recording method and a novel thermal recording sheet therefor.

Another object of this invention is to provide a novel method of converting a thermal pattern to a visible image and a recording sheet therefor.

A further object of this invention is to provide a novel method of converting a thermal pattern applied to a thermal recording sheet to a reversible latent image and then converting the resulting reversible latent image to an everlasting image.

Still another object of this invention is to provide a novel method of producing a transparent, light and highly pure color image.

A still further object of this invention is to provide a novel thermal recording method and a material therefor for producing multicolor images.

Still another object of this invention is to provide a novel thermal recording method and a material therefor for regenerating a continuous tone.

A still further object of this invention is to provide a novel thermal recording method and a material therefor for applying a thermal pattern to a thermal recording sheet and then forming a latent image which can be eliminated if desired.

Still another object of this invention is to provide a novel thermal recording method and a material therefor in which add-on is possible. I

A still further object of this invention is to provide an inexpensive thermal recording sheet and a process for production thereof.

According to one aspect of this invention, there is provided a thermal recording method which comprises applying a thermal pattern to a recording member having a recording layer composed of at least a polymer complex to produce a reversible latent image capable of being visualized.

According to a further aspect of this invention, there is provided a thermal recording method as mentioned above in which the polymer complex has a weak bond capable of being dissociated at a temperature ranging from 50C to l2O"C.

According to a further aspect of this invention, there is provided a thermal recording method mentioned above in which the resulting latent image is visualized with a dye liquid developer.

According to a further aspect of this invention, there is provided a thermal recording method as mentioned 4 above in which the latent image is visualized by utilizing difference of solubility.

According to a further aspect of this invention, there is provided a thermal recording method mentioned above in which the resulting latent image is visualized by utilizing difference of gas permeability.

According to a further aspect of this invention, there is provided a thermal recording method which comprises applying a thermal pattern to a recording member having a heat sensitive layer comprising a complex of polymers which are selected from polymers and copolymers of N-vinyl lactams, N-vinyl cyclic carbamates, N-vinyl imidazoles, 2-vinylpyridine, alkylene oxides, 4-vinyl-pyridine and acrylamide, to form a reversible latent image capable of being visualized.

According to a further aspect of this invention, there is provided a thermal recording method as mentioned above in which the resulting latent image is visualized with a dye liquid developer.

According to afurther aspect of this invention, there is provided a thermal recording method as mentioned above in which the resulting latent image is visualized by utilizing difference of solubility.

According to a further aspect of this invention, there is provided a thermal recording method as mentioned above in which the resulting latent image is visualized by difference of gas permeability. I

According to a further aspect of this invention, there is provided a thermal recording member used for the thermal recording method mentioned above which comprises a heat sensitive layer containing, as an active component, a polymer complex having a weak bond capable of being dissociated at a temperature ranging from 50C to 120C.

According to a further aspect of this invention, there is provided a thermal recording member used for the thermal recording method as mentioned above which comprises a. heat sensitive layer containing a complex composed of a low molecular weight compound or a polymer with a polymer selected from polymers and copolymers of N-vinyl lactams, N-vinyl cyclic carbak mates, N-vinyl imidazoles, 2-vinyl pyridines, alkylene oxides, 4-vinyl pyridines and acrylamide.

According to a further aspect of this invention, there is provided a thermal recording member used for the thermal recording method mentioned above which comprises a heat sensitive layer containing a polymer complex and a proton acceptor or a proton donor.

According to a further aspect of this invention, there is provided a thermal recording member used for the thermal recording method as mentioned above which comprises a heat sensitive layer containing a proton acceptor or proton donor and a complex composed of a low molecular weight compound or a polymer with a polymer selected from polymers and copolymers of N- vinyl lactams, N-vinyl cyclic carbamates, N-vinyl imidazoles, 2-vinyl pyridines, alkylene oxides, 4-vinyl pyridines and acrylamide.

According to a further aspect of this invention, there is provided a thermal recording member used for the thermal recording methodas mentioned above which comprises a heat sensitive layer containing an aliphatic or aromatic ketone which is non-volatile at room temperature and a complex composed of a low molecular weight compound or a polymer with a polymer selected from polymers and copolymers of N-vinyl lactams, N- vinyl cyclic carbamates, N-vinyl imidazoles, 2-vinyl pyridines, alkylene oxides, 4-vinyl pyridines and acrylamide.

According to a further aspect of this invention, there is provided a thermal recording member used for the thermal recording method as mentioned above which comprises a heat sensitive layer containing benzophenone and a complex composed of a low molecular weight compound or a polymer with a polymer selected from polymers and copolymers of N-vinyl lactams, N- vinyl cyclic carbamates, N-vinyl imidazoles, 2-vinyl pyridines, alkylene oxides, 4-vinyl pyridines and acrylamide.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a combination of an infrared absorption spectrum of PVP and that of ES-425 at a range of 1600 l800 cm;

FIG. 2 shows an infrared absorption spectrum of a complex of PVP and ES-425; and

FIG. 3 shows an infrared absorption spectrum directly after heating the complex in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention. there is provided a thermal recording method which comprises applying a thermal pattern to a thermal recording sheet to form a latent image, and contacting with a dye liquid developer, washing off with'a solvent, or utilizing the difference of gas permeability to convert the latent image to a visible image. The thermal pattern may be applied by a known method.

Representative methods for applying a thermal pattern are as follows.

1. Mechanical method A thermal recording sheet surface is partly and selectively heated by a heat stylus, a heat typewriter, a thermal printing head, or a scanning beam such as laser and electron beam. For example, a stylus heated by a nichrome wire is driven in accordance with an input signal to scan the surface of the thermal recording sheet and there is obtained a recording corresponding to the trace of the stylus. A thermal printing head is composed of a matrix of minorheating dots and the dots are selectively heated byapplying an electric current from a controlling circuit. A thermal recording sheet contacting the head is heated in accordance with the letter [or sign pattern to produce a record. Details and specifications of such thermal printing heads are disclosed in \U.S. Pat. No. 3,161,457 (National Cash Register) and Japanese Patent Publication No. 23520/1970. These "thermal printing heads may be used in the thermal re- 'ii cordingmethods of this invention.

Radiation heating method An original having a letter or sign pattern capable of absorbing a radiation is placed in contact with a thermal recordingsheet in a thermal conductive position and irradiated with a strong radiation such as an incanldescent tungsten lamp. The letter or sign portion of the i original absorbs more radiation than the background ruon and is more heated to raise the temperature -Qand thereby there is formed a thermal pattern, which is [then transferred to a thermal recording sheet by conduction' of heat.

,When athermal recording sheet having a radiation g -'absorption property is used and subjected to an extremely strong radiation for a short time by using a Tflashing discharging lamp as the radiation source for 6 heating, there can be effected a negative-positive reproduction. In other words, when such a thermal recording sheet is contacted with a negative image of a silver salt film and exposed to a flash discharging lamp on the film side, the radiation passing through transparent portions of the film is converted to heat in the thermal recording sheet to produce a thermal pattern. Upon producing a thermal pattern by laser beam scanning as mentioned in the mechanical method above, it is preferable to use a thermal recording sheet having radiation absorption property (absorbing said laser light wave length in this case).

Conversion of a latent image to a visible image is explained below. A thermal pattern is applied to a thermal recording sheet of the present invention by a method as mentioned above to produce a reversible latent image and then the resulting latent image is converted to a visible image within a period of life time. The life time of the latent image is a parameter showing reversibility of the latent image and is defined as a period of time from applying a thermal pattern to the maximum time at which any substantial lowering of density is not observed when developed, or a period of time from the application of a thermal pattern to a time at which the latent image is almost eliminated down to a fog density. One of these two definitions is used for each particular purpose.

A thermal recording sheet is contacted with a dye liquid developer to convert a latent image to a visible image. For example, the sheet is soaked in a dye liquid developer, or the sheet surface is wetted with a sponge, felt, roller or belt impregnated with a liquid developer, or a liquid developer is sprayed onto the sheet surface. It is also desirable to use a simple developing device such as a wet diazo copying machine and a developing device for a copier of a diffusion transferring reversing method, which may be used without any particular modification.

Necessary developing time varies depending upon the type, composition or temperature of the liquid developer or the mechanical conditions.

The developing time may be selected with a considerable latitude, but is in general, about 5 seconds taking into consideration rapid and access or about one minute for the purpose of reproduction of a continuous tone in the following examples.

At completion of development the image is already produced at a portion corresponding to the high temperature portion of the thermal pattern.

The recording is finished with or without washing with water to remove excess liquid developer. If desired, additional treatments of the images such as dry-- ing, chelating the dye image to improve the durability may be applied.

Latent images on one thermal recording sheet may be developed with two or more dye liquid developers to form each different colored image.

It is also possible to develop only the necessary portion of the latent images without developing the unnecessary portion thereof. The latent image not developed disappears by standing and said portion may be used again to reproduce other images.

In addition, the latent image may be visualized by utilizing'a difference of solubility in a solvent or a difference of gas permeability. Increase in solubility in a certain solvent of the latent image portion according to the present invention is observed.

Furthermore, increase in gas permeability is also ob-. served. Therefore, it is possible to form a relief image or colored image bywashing off with a solvent after formation ofthe latent image.

Alternatively, it is also possible to forma visible image by placing the recording sheet in a gas suchas ammonia gas after forming the latent image and forming color of a visible image forming component, in or under the recording layer, capable of forming color by alkali. The visible image forming component capable of forming color by alkali-may be a pH indicator or a combination of an aromatic diazo compound and a coupler.

The thermal recording sheet may be produced by providing on a support a thin film composed of a high polymer complex having a weak bond capable of being dissociated at 50C 120C. 7

By polymer complex is meant a complex compound of at least two kinds of polymer compounds, or at least one polymer and at least one low molecular weight compound having a moiety as described in Table l and Table 3 and there exists a weak bond between these components, and further, physical or chemical property of one or more of the components is remarkably changed. If there exists no bond among such components at all, the physical property of the mixture of the components is a simple sum of the physical or chemical properties of each component- The weak bond changes the physical or chemical properties of the components, but does not change the intrinsic chemical structure of each component substance.

In addition, the polymer complex includes a polymer having at least two kinds of moieties as shown in Table l and Table 3 in the same molecular chain. Such a polymer shows physical or chemical properties similar to a complex produced by mixing polymers having each moiety. V

In other words, the polymer complex in the present invention may be defined as follows:

1. complex composed ofa proton donative polymer and a proton acceptive polymer,

2. complex composed of a proton donative polymer and a proton acceptive low molecular weight compound,

3. complex composed of a proton acceptive polymer and a proton donative low molecular weight compound, and

4. polymer having a proton donative group and a proton acceptive group.

In items l (4) above, the proton donative moiety and the proton acceptive moiety are selected from moieties as shown in Table l and Table 3.

The cause of the weak bond has not yet been deter- I mined, but it is considered that the weak bond is caused by the complicated combination of electrostatic forces between ions, hydrogen bonds, van der Waals forces, electrostatic forces caused by partial transferring of electric charge or a spacial intertwinement of high polymer chains and segments.

In any event, it is essential that the bond be broken or relaxed at 50C 120C.

It is considered that an important factor of the complex of the present invention is hydrogen bonding or a spacial configuration based on entwinement of hydrogen bonding and molecular chains.

Table 1 illustrates atoms and atomic groups participating in the formation of the hydrogen bond. When 8 the proton donative compounds are combined with proton acceptive compounds, there may be formed complexesl' Table 1 Atoms and Atomic Groups participating in the formation of hydrogen bond Proton donative group Proton acceptive atoms or atomic (R is alkyl and/or aryl.)

of the molecule and its spacial configuration as well as hydrogen bonding are important and effective in the present invention. The polymer chains (intertwinement effect) probably delay the thermal dissociation speed of the weak bond to extend the life of the latent image enough to retain the life up to'the developing step, and when the latent image is maintained at a temperature higher than the temperature at which the polymer chain is frozen the latent image disappears gradually as the result of Brownian motion of the polymer chain. Room temperature is generally higher than the polymer chain freezing temperature.

Table 2 shows energy of typical hydrogen bonds. Since the energy value is about several Kcal./mole, it is clear that the bond can be easily cut by thermal energy.

, Table 2 Bond Energy of Hydrogen: Bond Type of From a quantitative point of view, the equilibrium constant of dissociation of many hydrogen bond complexes usually increases as the temperature is raised. In other words, this means that the complexes are dissociated to each component substance as the temperature is elevated. Table 3 illustrates some examples of fundamental structures of compounds capable of forming a hydrogen bond complex. I

According to the thermal recording method of the present invention, a, latent image is effectively produced by applying a thermal pattern at 50 C. Therefore, it is considered that the weak bond is dissoas mentioned above 7 V Fundamental Structure of Compound of Forming Hydrogen Bond Complex Proton donative (donor) group:

-T-fi --Cl) Ar-N-H ArN-R R-lT-R -(|3=(|I -C a (I: S HO, H", H H ..HR H, 1 o o '0 a I 0 0 o n O Q Q Q 0 i O I O I O I I O Proton acceptive (acceptor) group:

-N=N- H-O -NH., -NHR -OR I 0 O C I II Q I) I R N- t -c -'N -o- CN 47-012 N I II t 0 1| R N- o O O O o o a O G O I O II 0 Q where R is hydrogen, alkyl and/or aryl.

Has not yet been clearly proven that the bond of the polymer complex used in this invention is a hydrogen bond only, but to say the least, the combination of compounds having the moiety as shown in Table l and Table 3 is effective in the present invention.

According to an embodiment of the present invention, the thermal recording sheet of the present invention may be produced by providing on a support a thin film composed of at least a polymer (A) selected from polymers and copolymers of N-vinyl lactams, N-vinyl cyclic carbarnate, N-vinyl imidazole, 2-vinyl pyridines, 4-vinyl pyridines, alkylene oxides and acryl amide and a polymer (B) capable of forming a complex with the polymer (B). The polymer (A) as mentioned above can form a complex with other many substances.

When there'are mixed the solutions of .the polymer (A) and the polymer (B) in solvents such as water, alcohols, lower ketones, dioxanes and the like, there occurs a remarkable increase of the viscosity or formation of gel. When the polymer (A) and the polymer (B) are mixed and a thin film is produced from the mixture, dye acceptability of the polymer (A) in the thin film thus produced is masked and therefore, this thin film can not be dyed by a dye liquid developer capable of dyeing the polymer (A). The resulting film shows such a peculiar physical property, but when the film is treated with an acid or alkali or the pH is changed, the original components, that is, the polymer (A) and the polymer (B), can be recovered again from the thin film or gel. This factindicates the presence of a weak bond.

The polymer (B) capable of forming such a weak bond with the polymer (A) may be selected from many high polymers as mentioned later. The formation of the complex may be judged based on the above mentioned matter upon selectingpolymer (B).

When the above mentioned complex is heated to a temperature higher than a certain temperature, the complex can be dyed by the liquid developer. This mechanism is not yet clear, but may be considered follows. The polymer complex composed of a polymer (A) and a polymer (B) is stable at room temperature and the dye acceptability of the polymer (A) is masked and cannot be dyed by the dye liquid developer. However, the complex is dissociated to each component substance at a certain temperature or higher than said temperature and the physical properties of each component substance appear again to recover the dye acceptability of the polymer (A). The dissociation to each component seems to be accompanied simultaneously by separation of micro phase. The high polymer components thus dissociated coagulate each other by the self coagulation force and there is formed an island structure of one of them in a sea of the other (seaisland structure of a blend polymer), and thereby there is provided a surface sufficient to accept a dye from the dye liquid developer.

Each component dissociated at a high temperature returns again to a stable complex structure as the temperature is lowered and the dye acceptability is lost. The reversibility of the latent image of the thermal recording sheet of the present invention seems to be due to the above-mentioned reason. Rearrangement of the polymer segments requires a certain period of time so that the latent image can be present for a certain period of time.

The above mentioned explanation of the mechanism is given for the purpose of enabling one skilled in the art to understand this invention, but should not be construed as a limitation of the present invention.

Representative polymers (A) in this invention are: l. N-vinyl lactam polymer Polymers such as N-vinyl pyrrolidone, N-vinyl-3- methyl pyrrolidone, N-vinyl-S-methyl pyrrolidone, N- vinyl-3,3,5-trimethyl pyrrolidone, N-vinyl-3-benzylpyrrolidone, N-vinyl piperidone, N-vinyl-4-methyl piperidone, N-vinyl caprolactam (N-vinylhexahydro-2l-l-adipin-Z-one), N-vinyl capryllactam, N-vinyl-3-morpholinone, N-vinyl thiopyrrolidone, N-vinyl-Z-pyridone and the like.

The above-mentioned monomers are known materials and processes for the polymerization thereof are also known. Particularly important and commercially available homopolymers are poly-N-vinyl pyrrolidone, poly-N-vinyl piperidone, poly-N-vinyl caprolactam and poly-N'vinyl morpholinone. Copolymers of said monomers with each other or of said monomers with other vinyl monomers are also useful. The other vinyl monomer may be methacrylates, acrylates, acrylamides, acrylonitrile, vinyl ethers, vinyl acetate, vinylimidazoles,

1 1 ethylene and the like. Particularly, copolymers with vinyl acetate are commercially available. Also, the copolymer may include graft-copolymers, for example graft-copolymers of monomers such as formaldehyde, vinyl chloride, acrylamide, vinyl pyridine and the like onto poly-N-vinyl pyrrolidone.

2. N-vinyl cyclic carbamate polymer Polymers of monomers such as N-viny1-2-oxazolidone, N-vinyl--methyl-2-oxazolidone, N-vinyl-S- ethy1-2-oxazolidone, N-vinyl-4-methyl-2-oxazolidone, N-vinyl-2-thiooxazolidone, N-vinyl-2-mercaptobenzothiazole and the like.

Homopolymers of the above mentioned monomers or copolymers of the above mentioned monomers with styrene, vinyl acetate, methacrylate, vinyl ether, N- vinylpyrrolidone and the like are also included. Homopolymers of monomers such as N-vinyl-2-oxazolidone and N-vinyl-S-methyl-2-oxazolidone, or copolymers of these monomers with vinyl acetate are particularly important.

3. Polymers of N-vinyl imidazoles Copolymers of monomers such as N-vinyl imidazole, N-vinyl-2-methyl imidazole and N-vinyl-4-methyl imidazole, with other vinyl monomers such as styrene, acrylonitrile, methyl methacrylate, N-vinylpyrrolidone and the like. 4. 2-, or 4-Vinylpyridine polymer 5. Alkylene oxide polymer Polyethylene oxide, polypropylene oxide and the like. I 6. Acrylamide polymer Homopolymers or copolymers of methacrylamide and other alkyl or N-alkyl derivatives. There may be mentioned, for example, polyacrylamide, -methacryl amide, poly-N-methyl acrylamide, poly-N-normal butyl acrylamide, poly-N-benzyl acrylamide and N-methyl acrylamide N-butyl acrylate (1 l copolymer).

A thin layer of a homopolymer of N-vinyl lactam, N- vinyl cyclic carbamate, N-vinylimidazoles, 2- or 4- vinylpyridine, alkyleneoxide or acryl amide as mentioned above can be dyed by a dye liquid developer of this invention. 1n the case of a copolymer of the monomer with other vinyl monomers, the type of partner monomer and the composition ratio should be carefully selected to impart a suitable capacity of accepting a dye from a dye liquid developer. In the case of monomer such vinyl acetate, giving a water insoluble polymer, the developing speed by a dye liquid developer in the copolymer is retarded. Therefore, for example, in the case of a copolymer of N-vinyl lactam the composition ratio of N-vinyl lactam/vinyl acetate preferably ranges from about 60 40 to 90 10. On the contrary, when N-vinyl imidazole, N-vinyl pyridine and the like are copolymerized with N-vinyl lactam, the developing speed by a dye liquid developer is accelerated.

ln this manner, the developing speed or image density and the like may be controlled by appropriately selecting the partner monomer in copolymerization.

Polymers of N-vinyl lactam, N-vinyl cyclic carbamate, N-vinyl imidazole, 2- or 4-vinyl pyridine, alkylene oxide or acrylamide as aforementioned are made into a thin layer by combining with a polymer (B) forming the complex. Polymer (B) may be selected from high polymers of various kinds. Particularly, high polymers having carboxylic acid radicals, sulfonic acid radicals or OH radicals are preferable. Combination of polymer (A) and polymer (B) may be effected based on a standard that a complex is formed between them (the 12 examination of complex formation is disclosed previously). It is desirable to satisfy at least the following conditions. i

lfThe high polymer complex obtained is soluble in 5 usual solvents. This property enable one to form a thin layer of the complex from the solvent solution. 2. When the high polymer complex solution is coated and dried on a support, a homogeneous and substantially transparent layer is formed without separating the components from each other.

The examination whether the above mentioned conditions are satisfied may be carried out easily by those skilled in the art.

Further, the examples of useful polymer (B) in this invention are shown as below.

1. Polymer having carboxylic acid radical; for example:

A. Polyesters obtained by reacting an excess of aliphatic polyhydric carboxylic acid such as citric acid, tartaric acid and the like with diols such as ethylene glycol, 1,4-butanediol, diethylene glycol, dipropylene glycol and the like.

B. Acid cellulose derivatives shown in the following Table 4.

Table 4 Acidity Total of of substisubsti- Polymers tution tution 3O Cellulose-propionate/ 2.0 1.0

h dr 5 en scbacinate y K g Cellulose-acetate] methacrylatc .5 08

hydrogen succinate Cellulose-acetate crotonate V 2.6 (1.)

hydrogen phthalate I Cellulose-benzoate 1 1.2 hydrogen tercphthalatc Cellulose-cyclohexane carboxylate 2.1 1.0

hydrogen oxalate Ccllulosc-nptrate hydrogen phthalatc 2.6 0.8 Methyl cellulose-hydrogen phthalate 2.3 0.7 Cyclohcxyl cellulose-hydrogen succinate 2.1 0.8 C yanoethyl cellulose- 2.5 0.8 40 hydrogen succinate Ethyl cclluloscacetatc 2.8 0.8

hydrogen succinate Cyunoethyl cellulosestcarate 2.2 1.0

hydrogen phthalatc Bcnzyl cellulose-hydrogen succinate 2.3 1.0 Hydroxycthyl cellulose-acetate 2.5 0.7 hydrogen succinate Cellulose-butyratc 2.0 1.0

hydrogen succinate hydrogen phthalatc Ethyl cellulose-hydrogen succinate 2.8 1.0

hydrogen maleate C. Acid polyvinyl polymer (The process for producing them is disclosed-in Japanese Patent Application No. 8495/ 1960 by DuPont Co. Ltd.)

There may be mentioned, for example, polyvinyl hydrogen oxalate, polyvinyl hydrogen malonate, polyvinyl hydrogen glutarate, polyvinyl hydrogen adipate, polyvinyl hydrogen suberate, polyvinyl hydrogen maleate, polyvinyl hydrogen undecenyl succinate, polyvinyl hydrogen isophthalate, polyvinyl hydrogen terephthalate, polyvinyl hydrogen hexahydrophthalate, polyvinyl- O-carboxymethylphenyl acetate, polyvinyl-P-carboxymethylphenyl acetate, polyvinyl-O-carboxyphenyl acetate, polyvinyl hydrogen succinate polyvinyl hydrogen phthalate (90/10), polyvinyl hydrogen oxalate polyvinyl hydrogen isophthalate (50/50), polyvinyl hydrogen maleate [polyvinyl hydrogen adipate 10/90), polyvinyl acetate polyvinyl hydrogen succinate 13 (70/30), polyvinyl benzoate polyvinyl acrylate polyvinyl hydrogen succinate( 4l/ 4/5,5), polyvinyl formate polyvinyl hydrogen terephthalate (65/35), polyvinyl propionate polyvinyl hydrogen phthalate (40/60), polyvinyl alcohol polyvinyl hydrogen phthalate (10/90), polyvinyl alcohol polyvinyl hydrogen succinate (19/81), polyvinyl alcohol polyvinyl hydrogen glutarate (29/71), polyvinyl alcohol polyvinyl hydrogen maleate (65/35), polyvinyl alcohol polyvinyl acetate polyvinyl hydrogen isophthalate 10/60/30), polyvinyl alcohol polyvinyl propionate polyvinyl hydrogen maleate (15/45/40), polyvinyl alcohol polyvinyl acetate polyvinyl hydrogen maleate 30/ 10/60), polyvinyl alcohol polyvinyl acetate polyvinyl hydrogen maleate (29/34/37), polyvinyl alcohol polyvinyl acetate polyvinyl hydrogen succinate 16/13/71 polyvinyl chloride polyvinyl acetate polyvinyl hydrogen succinate (25/25/50), polyvinyl chloride polyvinyl acetate polyvinyl methacrylate polyvinyl hydrogen succinate (20/ 15/5/60), polyvinyl chloride polyvinyl butyrate polyvinyl hydrogen maleate (30/30/40), polyvinyl alcohol polyvinyl chloride polyvinyl acetate polyvinyl hydrogen phthalate /15/70), ethylene/ vinyl acetate vinyl hydrogen succinate copolymer (4/42/54), ethylene vinyl benzoate vinyl hydrogen succinate copolymer (5/40/55), propylene vinyl acetate vinyl hydrogen maleate copolymer (4/46/50), ethylene vinyl acetate vinyl hydrogen glutarate copolymer /40/45), ethylene vinyl alcohol vinyl acetate vinyl hydrogen succinate copolymer (5/5/40/50), ethylene vinyl alcohol vinyl acetate vinyl hydrogen phthalate copolymer (2/22/9/67), polyvinyl formal polyvinyl hydrogen glutarate (50/50), polyvinyl butyral polyvinyl hydrogen allylsuccinate (60/40), polyvinyl propional polyvinyl hydrogen maleate (65/35 polyvinyl formal polyvinyl acrylal polyvinyl hydrogen succinate (50/10/40), polyvinyl butyral polyvinyl hydrogen adipate (50/50), polyvinyl benzal polyvinyl hydrogen phthalate (50/50), polyvinyl benzoate polyvinyl-P-carboxybenzal (40/60), polyvinyl butyral polyvinyl hydrogen phthalate (40/60), polyvinyl formal polyvinyl acetal polyvinyl hydrogen terephthalate (40/30/40), polyvinyl formal polyvinyl butyrate polyvinyl carbonate polyvinyl hydrogen succinate (40/10/10/40), polyvinyl formal polyvinyl methylether polyvinyl hydrogen phthalate (40/10/50), polyvinyl acetate polyvinyl ethylether polyvinyl hydrogen succinate (60/10/30), polyvinyl benzal polyvinyl methylether polyvinyl hydrogen diglycolate (45/30/25), polyvinyl butyral polyvinyl hydroxyether polyvinyl hydrogen glutarate (60/10/30), polyvinyl alcohol polyvinyl formal polyvinyl B- cyanoethylether polyvinyl hydrogen phthalate (5/20/25/50), poly-N-vinyl-N-methylformamide vinyl acetate vinyl hydrogen succinate (30/30/40), poly-N- vinyl-N-methylformamide vinyl acetate vinyl hydrogen phthalate (15/40/45), poly-N-vinyl-N-methylformamide vinyl acetate vinyl hydrogen glutarate (40/ 15/45), poly-N-vinyl-N-methylacetamide vinyl acetate vinyl hydrogen succinate vinyl hydrogen maleate (30/30/30/10), poly-N-vinylphthalamide vinyl methacrylate vinyl acetate vinyl hydrogen succinate (5/25/30/40), poly-N-vinyl caprolactam vinyl acetate vinyl hydrogen phthalate (/30/50), poly-N-vinyl-N- methylformamide vinyl formal vinyl acetal vinyl hydrogen succinate (20/30/20/30), poly-N-vinyl-N- methylacetamide vinyl methacrylate vinyl acetate vinyl acetal vinyl hydrogen phthalate 10/ l 0/ 20/ 20/40), poly-N-vinyl-N-methylbenzamide vinyl acetate vinyl formal vinyl hydrogen succinate vinyl hydrogen maleate (10/25/ 15/40/ 10), poly-N- vinylpyrrolidone vinyl acetate vinyl formal vinyl hydrogen succinate (10/20/30/40), poly-N-vinyl-N- methylformamide vinyl alcohol vinyl acetate vinyl hydrogen succinate (20/5/35/40), poly-N-vinyl-N- methylformamide vinyl alcohol vinyl acetate vinyl hydrogen phthalate (10/25/15/50) and the like.

D. Acrylic acid and methacrylic acid polymer There may be mentioned, for example, polyacrylic acid, partially hydrolyzed product of polymethacrylic acid-n-butyl, partially hydrolyzed product of polyacryl- N-n-propylamide and the like.

E. a,B-Unsaturated acid polymer There may be mentioned, for example, polymers of a,B-unsaturated acids such as maleic anhydride, itaconic anhydride, citraconic anhydride, diester fumarate and the like, or copolymers of the a,B-unsaturated acid as mentioned above with other vinyl monomers. Vinyl monomers to be copolymerized with the acid anhydride monomer preferably include vinyl esters such as vinyl acetate andthe like and vinyl ethers. Vinyl monomers to be copolymerized with diester fumarate is preferably include acrylamide, vinyl esters, vinyl ethers, ethylene, styrene, acrylic esters and the like.

The above mentioned polymer is disclosed in Murahashi, lnoue and Tani, Gosei Kobunshi [111], Asakura Shoten, 1971, pages 250-257 and pages 374-380. Among them, a particularly useful polymer is maleic anhydride copolymer since it is not expensive. A carboxylic acid radical existing in the copolymer forms the derivatives such as the mono ester of dicarboxylic acid, mono amide and the like by reacting with a compound having active hydrogen such as alcohol, ammonia, primary and secondary amines and the like. Also, the derivatives thereof are useful in this invention. Processes for producing some of them are disclosed in the following US. Patents.

For example,

A. Acid cellulose derivatives Table 5 shows some representative examples.

Table 5 Total of Acidity of substisubsti Polymers tution tution O ethyl cellulose-acetate 2.6 0.9 hydrogen succinate hydrogen phthalate Cellulose'acetate hydrogen 2.65 0.85 sulfate hydrogen phthalate Ethyl cellulose-hydrogen-O- 2.2 0.5 sulfobenzoate O-P-sulfonbenzile cellulose- 2.6 0.8

Table -continued Total of Acidity of cellulose-acetate The process of preparation thereof is disclosed in Japanese Publication No. 5093/1960 (DuPont Co. Ltd.).

B. Acid polyvinyl alcohol derivatives For example, polyviny1-0-su1fobenzoate, polyvinyl-B- sulfopropionate, polyvinyl-B-sulfovarate, polyvinyl-P- sulfophenyl acetate, polyvinyl acetate polyvinyl-O-sulfobenzoate (50/50), polyvinyl benzoate polyvinyl-ysulfopropionate (50/50), polyvinyl acetate polyvinyl crotonate polyvinyl-2-sulfo-4-carboxybenzoate (40/30/30), polyvinyl formal polyvinyl butyral polyvinyl-p-sulfobenzal (/60/30), polyvinyl formal polyvinyl acetate polyvinyl-O-sulfobenzal (60/20/20), polyvinyl alcohol polyvinyl acetate polyvinyl formal polyvinyl-O-sulfobenzal (5/40/30/25),- poly-N-vinyl- N-methylformamide vinyl acetate vinyl-O-sulfobenzoate (30/30/40), poly-N-vinyl-N-methylacetamide vinyl acetate vinyl-B-sulfopropionate (40/30/30), poly-N-vinyl-N-methylformamide vinyl alcohol vinyl acetate vinyl-O-sulfobenzoate (lO//40/30) and the like.

3. Polymer having OH radical; For example,

A. Particularly, cellulose ethers,

For example, ethyl cellulose, benzyl cellulose, hydroxyethyl cellulose, hydroxyethyl ethyl cellulose, hydroxyethyl benzyl cellulose and the like.

B. Phenolic resin;

Particularly, resol-type solvent-soluble phenol or cresol-formaldehyde resin and phenoxyacetic acid-formaldehyde resin.

Polymer (A) and polymer (B) as mentioned above are properly selected and combined in accordance with the aforementioned conditions. That is, at least a high polymer selected from the polymer (A) group and at least a high polymer selected from the polymer (B) group are mixed in a solution form and the complex thus formed is separated (when the solvent is water, alcohol, ketones and the like, the complex may be normally separated as gel), dissolved in a solvent for the complex, thereafter coated on a support and dried to form a thin layer. Alternatively, from the first each high polymer is dissolved and mixed in a solvent for the complex, coated on a support and dried to form a thin layer. In order to improve various responses to heat or a physical property of the film of the thermal recording layer, a third inert polymer or plasticizers may be added. These substances are selected from known materials.

For the purpose of facilitating the selection of the high polymers, combinations of high polymers and various embodiments of heat sensitive sheets made therefrom are shown in Example 7. An example of polymer (B) giving a preferable result when combined with a polymer (A) is a,B-unsaturated acid polymer, particularly, a copolymer of an alkyl vinyl ether and maleic anhydride. Thee combination of the above-mentioned polymer (B) and the polymer (A) provides a thermal recording sheet having excellent film physical proper- 16 ties such as flexibility, mechanical strength and the like and satisfyingrequiredcharacteristics such as heat sensitive temperature, image density, contrast, clearness of background and the like without adding any other third component. v 1

Examples of appropriate copolymers of alkyl viii,

ether and maleic anhydride are mono esters [l], mono ammonium salts [11] and mono amides [111] of vinyl ethers having alkyl radical of C -C maleic anhydride copolymer (copolymerization ratio being 'about 1:1). When copolymerization ratio is 1:1, the unit structure is represented as follows:

(Ill) wherein R and R are alkyl radicals having C C R R is hydrogen or an alkyl radical having C C and the total carbon atoms of R R, and R and R R is not more than 19.

CHTH

and maleic anhydride are polymerized in the presence of a peroxide by the process, for example, M. lmoto, K. Satomi, J. Polymer Sci., 31 208 (1960), to produce an alkyl vinyl ether maleic anhydride copolymer [V]. Though the copolymerization ratio is somewhat different depending upon the type of vinyl ether or polymerization conditions, this is about 1:1.

11 1: EZTEZTF Examples of suitable alkyl vinyl ethers are shown below. Only the alkyl radical R is illustrated. The number in the parentheses is the boiling point: methyl (6.0), ethyl (35.5), n-propyl (655), i-propyl (55), n-butyl (94), i-butyl (83), t-butyl i-amyl (109), nhexyl (143), n-octyl (58, 44 mmHg), 2-ethyl hexyl (177), n-decyl (101, 11 mmHg), n-dodecyl (126, 3 mmHg), n-octadecyl (182, 3 mmHg). Some of them are already commercially available.

Alkyl vinyl ether maleic anhydride copolymer [V] is reacted with an alcohol under moderate conditions to produce a monoester.

Usually the copolymer. [V] and an excess of a correspondingalcohol are heated, and after the reaction is finished, [I] is;obtained byremoving the alcohol. In order to accelerate the reaction, if necessary, a small amount of a mineral acid such as hydrochloric acid, sulfuric acid and the like may be added. As the alcohol chain and branching increase, the heating period is extended, for example, 2 hours (at refluxingtemperature) for methyl alcohol and approximately 24 hours (at 100C, adding hydrochloric acid) for n-octadecyl alcohol.

Further, some of the methyl vinyl ether maleic acid mono ether copolymers are supplied by: General Aniline and Film Corp, for example, Gantrez ES Resin.

Mono ammonium salts [II] are obtained by neutralizing with ammonia or the corresponding alkyl amine after hydrolyzing the copolymer [V] and mono amides [III] are obtained by reacting ammonia or the corresponding primary or secondary alkyl amine with the copolymer [V].

The process for producing alkyl vinyl ether maleic anhydride copolymer and the derivatives thereof is shown below.

1. An example of a process for producing n-butyl vinyl ether maleic anhydride copolymer [VI] Desiccated refined benzene 1000 ml.) is poured in a three-necked flaskequipped with an agitator and a tube introducing nitrogen, and maleic anhydride 134 g.) and 135 g. of n-butyl vinyl ether (a reagent manufactured by Tokyo Kasei Kogyo K.K.) are dissolved therein, thereafter the substitution of nitrogen is carried out. Benzoyl peroxide 1.7 g.) is added thereto, ag itated for 4 hours at 50C 60C, then for hours at A gelatinous polymer is obtained and benzene is removed therefrom. The resulting matter iswashed sufficiently with ethylene dichloride and dried by removing water to produce 260 g. of a flocculent product.

The result of elementary analysis is C:61.5%,

H:7.20%. These data agree well with the calculated values as l/l alternate copolymer of n-butyl yinyl ether maleic anhydride, that is, C:60. 6%,- H:7. 06%. "17 in methyl ethyl ketone is approximately 1.2.

In the same manner, copolymers of approximately l/l ratio are obtained from i-butyl vinyl ether, i-octyl vinyl ether or noctadecyl ether and maleic anhydride.

then the pH value is reduced with dilute hydrochloric acid; The resulting precipitate is filtered, washed and dried to produce a white. flocculent product (9.5 g). The product is methyl vinyl ether/ maleic acid mono-noctyl ester.

. Elementary, analysis: C:61.9% (62.90%), H:8.5% (9.1%).

. In the same manner, mono-n-octadecyl ester [IX] is obtained by using n-octadecyl alcohol as a substitute for n-octyl ,alcohol. Elementary analysis: C: 68.8% (70.4%), I-I:9.9% 10.8%), wherein the values in parentheses are the theoretical values.

4. An example of a process for producing n-butyl vinyl ether maleic acid mono amide copolymer [X] [XIV].

Compound [VII] 10 g.) obtained in the above example, i.e. item 1, is dissolved in 100 ml. of acetone with agitating,and added to 200 ml. of a cold 20% aqueous ammonia solution. Then, the temperature is raised to 50C for 2 hours. After cooling and adjusting the pH value to 1.0 with 5% hydrochloric acid, the separated precipitate is filtered, washed and dried to obtain a white flocculent product (9.0 g.). The product is nbutyl vinyl ether maleic acid mono amide copolymer [X]. Elementary analysis: N:6.30% (6.50%) wherein the value in the parentheses is the theoretical value.

In the same manner, mono-N-methyl amide copolymer [XI] is obtained by using methyl amine as a substi- 2. An example of a process for producing n-butyl vinyl ether maleic acid mono ethyl ester' copolymer [VII].

The 10 g. of compound (VI) obtained in the above example is dissolved in 100 ml. of ethyl alcohol containing a drop of concentrated hydrochloric acid, and boiled'for 5 hours with removing water. Almost all of the alcohol is distilled at a reduced pressure, 'washed with a mixture of ether/hexane and dried to give 10g. of 1 a white flocculent product. Theproduct is n-butyl vinyl ether maleic acid mono ethyl ester copolymer [VII]. Elementary analysis: C:60.2% (59.0%), H:8.32% (8.20%), wherein the values in parentheses are the theoretical values.

3. An example of the process for producing methyl vinyl ether maleic acid mono-n-octyl ester copolymer [Vlll].

Methyl vinyl ether maleic anhydride copolymer 10 g.) (trade name, Gantrez A N 139, manufactured by General Aniline and Film Corp.) is dissolved in a solution of pyridine (100 ml.) in n-octyl alcohol (8.5 g.), agitated for 5 hours at 100C, poured into water, and

tute for aqueous ammonia. The elementary analysis value is N:5.85% (6.12%).

In the same manner, mono-N-i-propyl amide copolymer [XII] is obtained by using i-propyl amine. The elementary analysis value is N:4.95% (5.45%).

In the same manner, mono-N,N-diethyl amide copolymer [XIII] is obtained by using diethyl amine. The elementary analysis value is N:4.80% (5.15%) wherein the value in the parentheses is the theoretical value.

In the case of higher amines, the reaction is carried out in a solution of the amine in pyridine. Pyridine solution of n-hexyl amine (6.5 g.) is added to a solution of methyl vinyl ether maleic anhydride copolymer (10 g.) (trade name, Gantrez AN-l39, manufactured by General Aniline and Film Corp.) in ml. of methyl ethyl ketone. After reacting for 2 hours at 40C, most of the methyl ethyl ketone is distilled under reduced pressure and then dilute hydrochloric acid is added thereto. The resulting matter is washed with water and dried sufficiently to obtain 14.0g. of a white flocculent product. The elementary analysis value is N25. 1% (5.45%) wherein the value in the parentheses is the theoretical value. This product is methyl vinyl ether maleic acid mono-N-n-hexyl amide copolymer [XIV].

In the samemanner, by reacting Gantrez AN-l 19 (trade name) with N-methyl-N-n-octadecyl amine, there is obtained methyl vinyl ether maleic acid mono N-methyl-N-n-octadecyl amide copolymer [XV]. The elementary analysis value is N:2.7% (3.20%).

The aforementioned layer comprising the complex of polymer (A) and polymer (B) is manufactured by coating the solvent solution on a suitable support and drying. The complex may be produced by mixing the polymer (A) solution with the polymer (B) solution and recovering the separated complex. It is economical, however, that the polymer (A) and the polymer (B) are mixed, dissolved in a solvent capable of dissolving the complex, and directly used as a coating solution.

In the complex thin layer thermal recording sheet ac cording to this invention, various kinds of additives 19 20 other than the complex of polymer (A) and polymer FH HQ] RCOO C H QH CSH'SNHCOCH, (B) may be added. As the additives, there may be men- RCONHR, ROH, C H NHC H RCONH H O, tioned a flattening agent of the coating such as silica C1 CH aerogel (finely divided powder of SiO titaniumoxide 7 powder and the like, and an image property controlling 5 agent. It has been now found that some compounds have a powerful effect on the image property of this recording complex. In general, certain kinds of proton fi s 4; 5-. donors and proton acceptors may contribute to l reducing the back ground density, (2) decreasing the 10 NH image density and contrast, and (3) decreasing the de- (H2 veloping speed. Further, as these contribute to improvement in regeneration of the image and sharpness 5 z- CGHBCH2NH2- thereof, controlling the vanishing speed of the latent Proton accepting capacity: (arranged in order of inimage, and reducing the aging period after coating and tensity) R Gill-[Q RCON RCONHR' drying the recording sheet, and therefore the recording Ha- 2 nBt-O- RCHO. cu properties are improved.

The examples of proton donors and proton acceptors HO H CHPGH? are shown as follows.

Proton donative ca acit arra 55 p y nged in order of in z CHaCH=CH CHO tensity) c c R' I cH cooc H c CH 000 wherein R, R',R" and the like are alkyl or aryl.

These effects of the proton donor and proton acceptor seem to be based on a certain interaction of hydrogen bond affecting the bond between polymer (A) and polymer (B) or space configuration.

The above explained effect of image property controlling agent is shown in the Examples (infra).

In the foregoing there are explained in detail proton donative-polymers (A), proton acceptive polymers (B) and complexes thereof. The complex used for the present invention may be produced by combining one of the polymers (A) and the polymers (B) with a low molecular weight compound capable of forming a complex by combining with such polymers. The low molecular weight compound may be selected from compounds having a structure similar to the structure of the proton donative or proton acceptive monomer of the polymer (A) or (B).

When the complex of the polymer with the low molecular weight compound is used for visualizing by using a dye liquid developer, the dyeability of the polymer is a very important factor so that the polymer should be selected from polymers having dyeability. When a polymer (A) and a polymer (8') can form a complex, there may be often used a copolymer having monomer structures which constitute the polymer (A) and the polymer (B).

Explaining now about the dye liquid developer suitable for this invention, the latent image of the thermal recording sheet according to this invention is dyed by accepting selectively the dye from the dye liquid developer. There are many kinds of dye capable of being accepted. Whether a dye can be accepted is not always determined by its chemical structure. For example, whether there exists an anionic group or a cationic group is not a standard of selecting the dye, but whether the dye can dye one of the polymer components for the high polymer complex composing the recording sheet seems to be an important standard. It is practically preferred that the dye is relatively water-soluble.

The expression relatively water-soluble" as used herein means to be soluble in water alone or a mixture of water and an organic solvent miscible with water such as alcohol, lower ketone, dioxane, benzyl alcohol and the like.

The following are representative dyes suitable for this invention.

Triphenylmethane dye such as Rhoduline Blue 6GA, Brilliant Green, Malachite Green, Para Rosaniline,

liant Carmoisine O, Naphthol Red 0, Fast Light Orenge GX, Orenge IV, Mentanil Yellow and the like; anthraquinone dye such as Alizarine Astrol B, Alizarine Pure Blue B, Alizarine Cyanine Green G, Anthraquinone Violet, Anthraquinone Blue and the like;

ketoimine type dye such as Auramine O and Auramine G.

An aqueous solution of these dyes or an aqueous solution containing alcohol, lower ketone, dioxane and benzyl alcohol of these dyes may be used as a dye liquid developer. Further, a buffer solution for adjusting pH, or an inorganic salt such as sodium sulfate, sodium chloride and the like for controlling the dyeing capacity, or an organic mordant such as poly-N-vinyl pyridinium quaternary salt and the like other than the dye may be added to the dye liquid developer. When the complex obtained from a N-vinly lactam polymer and the like has an anionic radical such as a carboxylic acid radical or a sulfonic acid radical and the like, it is desirable that the pH value is neutral or acid for the purpose of decreasing the background density as far as possible.

Further, if necessary, there may be used an oil type dye such as Oil Brown N, Oil Red 0, Solvent Blue 16, Solvent Violet l7, Solvent Black 12 and the like. A negative image is generally obtained by using an oil type dye.

The above mentioned dyes are common dyes. However, the dye used for a dye liquid developer according to this invention is not limited only to a colored substance, but may include a substance such as a fluorescent substance, an ultraviolet ray absorber, an electron ray absorber and the like which produce an image by irradiation with ultraviolet rays and electron rays, and the like. Further, it should be understood that a liquid developer containing a substance capable of forming a colored substance by reaction with a third substance incorporated in the thermal recording layer is also within the scope of the dye liquid developer of the present invention. There may be mentioned, for example, a combination of a metal salt and a chelating agent and a combination of a diazo compound and an azo coupler (one of them is incorporated in either the thermal recording layer or the liquid developer). It is very easy to select a substance which is inert and not heat sensitivity when incorporated in the thermal recording layer.

The following examples are given to illustrate embodiments of the invention as it is presently preferred to practice it. It will be understood that these examples are illustrative, and the invention is not to be considered as restricted thereto.

EXAMPLE 1 30 g. of methyl vinyl ether maleic acid mono n-butyl ester copolymer [trade name: Gantrez ES-425 manufactured by GAF (General Aniline and Film Corp); solid content: 50%] was added to a solution of g. of poly-N-vinyl pyrrolidone (trade name: PVP, [(-90 manufactured by GAF) in 150 g. of alcohol and stirred to obtain a gel-like high polymer complex. 150 g. of dimethyl formamide was added to said gel-like complex to dissolve said gel-like matter and obtain a homogeneous and clear solution. A polyester film of 70 microns in thickness subjected to a treatment of imparting a hydrophilic property was coated with said solution and dried by hot air at 70 80C (the thickness of said coating was 2 microns after drying). The properties of said film such as its heat sensitive temperature or contrast may be stabilized after standing at room temperature (about C) for several days. Said produced thermal recording sheet was contacted with a thermal wedge composed of aluminum hot plates set at temperatures between 40C and 150C at intervals of 10C for about 3 seconds, then dipped in a dye liquid developer D-l (a solution of 0.5 g. of Crystal Violet in 100 ml. of distilled water) and washed with water. An image began to appear at 60C and showedabout maximum density at 70C. In other words, the initial changing temperature of said thermal recording sheet was 60C and the total changing temperature was 70C.

The process for preparing said high polymer complex solution is fairly optional. The polyester film coated with a solution of a copolymer of poly-N-vinyl pyrrolidone and mono-n-butyl ester in a mixture of 150 g. of alcohol and 150 g. of dimethyl formamide was a thermal recording sheet having the same properties as that of the above mentioned one.

The film surface of said thermal recording sheet was closely contacted with one side of a manuscript printed on both sides and passed through a Thermofax copying machine (Secretary type, manufactured by Minesota Mining and Manufacturing Co.). A visible change was scarcely found on said surface at this stage. A clear violet image appeared on the portion corresponding to letter portions of the manuscript when the thermal recording sheet was dipped in a dye liquid developer D-l (liquid temperature: 20C) and pulled up, and said image was fixed firmly on the sheet without any further treatment. Said image density was 1.54 (measured by a red filter) and the background density was 0.02. A transparent image having high contrast was formed by projecting said sheet using an overhead projector.

Table 6 shows the relation between standing time and image density when the thermal recording sheet of this Example was passed through a Thermofax copying machine with a black colored manuscript, allowed to stand at 20C (room temperature) for a predetermined time and then developed with said dye liquid developer D- 1.

up to developing after giving a thermal pattern Standing Time lmage density (red filter) directly after l.50 after l0 minutes L50 30 minutes L40 1 hour l.20

12 hours 0.10

24 hours 0.02

Table 6 shows the reversibility of a latent image formed on the recording sheet of this invention. It is found in Table 6 that the recording sheet of this invention can be used once more and add-on of other images is possible after standing for about 24 hours since the latent image disappears almost completely after standing for about 24 hours, and that it is possible to stock copies since the image density hardly changes at standing times of 10 30 minutes.

Table 7 shows the image characteristic when the solution of the high polymer complex of this Example was applied to a polyester sheet under the above conditions, dried and then allowed to stand at 20C (room temperature). The background density after standing at various times and developing in a dye liquid developer D] was measured (developed without passing through Thermofax copying machine).

Table 7 Relation between standing time and background density Standing Time Background Density (red filter) directly after 1.45 after 12 hours 0.50 24 hours 0.25 3 days 0.05 7 days 0.02 10 days 0.02

Table 8 shows that various dye liquid developers may be used for the sheet of this Example.

Table 8 Results developed in various dye developing solutions Liquid Density Developer Composition of Back Numher Liquid Developer lmage Ground Filter D-lll 0.20 0.00

D-lV 0.51 0.08 Red Note: Dipping in a liquid developer at 20C for 5 seconds There is an optimum range in composition ratio of the poly-N-vinyl pyrrolidone mono-n-butyl ester copolymer. Said range changes depending upon the formulation of the liquid developer and the temperature of the liquid developer. Table 9 shows the relation between the composition ratio of poly-N-vinyl pyrrolidone mono-n-butyl ester copolymer and the image I 25 property when developed with a D-l at 18C for 8 seconds. i

' Table 9 Relation betweenthe composition ratio of poly-N- vinyl pyrrolidone and methyl vinyl ether maleic acid mono-n-butyl ester copolymer and the image property dye liquid developer Amount (g.)

Gantrez [28-425 3 (Solid Density Sample PVP Content; Composition Back Number K-90 g. Ratio Image Ground 1 20 10 10 film was dissolved 2 l8 2 9/ I 1.50 L45 3 l4 6 7 3 1.40 0.60 4 ll 9 5.5 4.4 1.30 0.05 5 10 5 5 1.30 0.02 6 9. ll 4.5/5.5 L 0.02 7 6 l4 3 7 0.50 0.01 8 2 18 l 9 0.20 0.00 9 0 20 0/ 10 0.0 0.00

Some spectroscopic data of a specific polymer complex is shown. In FIG. 1, the infrared absorption spectrum of the complex of polyvinyl pyrrolidone (PVP) and methy vinyl ether maleic acid mono-n-butyl ester copolymer (ES-425) is shown.

A gel-like product is precipitated by mixing PVP and ES-425 in alcohol, washed with alcohol several times and dried to produce a white powdered complex. The complex always shows a constant elementary analysis regardless of the molar ratio of PVP to ES-425. The elementary analysis is as follows: C 58.02%, H 7.64%, N 4.71%. The molar ratio of PVP in said complex calculated value of the elementary analysis is 55%. In FIG. 2, absorption of carbonyl radical of pvp, 1680 cm and absorption of carboxylic acid of ES-425, 1715 cm", as illustrated in FIG. I disappear, and a new broad absorption having the peak at 1660 cm appears. Said new adsorption is considered to be the adsorption due to the shifting of the proton of carboxylic acid and carbonyl radical to the side of low wave member as the result of hydrogen bonding of proton of carboxylic acid and carbonyl radical. Hydrogen bonding is considered to contribute to the formation of said complex as shown in the following scheme.

C11, -COOH CII CII i N .7 i 1 5 (.11 LOO( H U 0 U 0 HOOC (1H H C OOC-CH (Complex) Next, the infraredabsorption spectrum of the complex of N-rnethyl pyrolidone and mono ethyl succinate the low wave number by hydrogen bonding of the car boxyl ic acid and carbonyl radicals, and both absorpftions of l715cm and 1685 cm disappear.

The formation of a latent image on a heat sensitive layer of this invention is explained by the infrared absorption spectrum as described above.

when a complex is partly heated, the physical and/or chemical properties of the heated portion are different from those of the portions which are not heated.

Changes in the physical and chemical properties in the heated portion are due to the change of bonding state between molecules constituting the complex, and this has been confirmed by infrared absorption spectra. For example, the complex produced from PVP and ES- 425 is formed by hydrogen bonding of the carbonyl radical of PVP and the carboxylic acid of ES-425 and thereby an absorption appears at 1660 cm" in an infrared absorption spectrum. FIG. 3 shows an infrared ab- .sorption spectrum directly after heating the complex. When the complex is heated, the absorption at 1660 cm changes to two sbsorptions at 1680 cm and 1640 cm", and a shoulder of absorption appears at 1715 cm. Since the absorption at 1680 cm corresponds to the position of the carbonyl radical of PVP which is not hydrogen bonded and the absorption at 1715 cm corresponds to the position of the carboxylic acid of ES-425, it is confirmed that the hydrogen bond is partially dissociated by heating.

When'said changed complex stands for a long time at room temperature, the bond of said complex by hydrogen bond recovers to provide the same infrared absorption spectrum as that of the initial complex. This phenomenon corresponds to disappearance of difference of physical and chemical properties of the complex.

In the foregoing, the spectroscopic properties and the mechanism of forming the latent image are explained with respect to only a specific example, but such specific example is used for the purpose of aiding in understanding of this invention and should not be construed as a limitation to the scope of the invention.

EXAMPLE 2 15g. of poly-N-vinyl pyrrolidone (trade name: PVP K-) and 14g. of methyl vinyl ether/maleic acid mono-N-n-hexylamide [XIV] were dissolved in a mixture of g. of alcohol and 150g. of dimethyl formamide. The resulting solution was applied to a semitransparent tracing paper (of a thickness of about 30 microns) in a thickness of about 2 microns and dried. Since the heat sensitivity of said product is stabilized after about 10 days, the said product was allowed to stand for said period, cut into a tape for contact with a heated printing head(a small computer manufactured by Canon Co., trade name: pocketronic) and the latter operated.

The surface of said tape was moistened with a felt absorbing the dye liquid developer D-IV used in Example 1 to print red clear figures. I

EXAMPLE 3 This Example relates to a sheet for stylus recording used in oscillograph recording. N-vinyl pyrrolidone polymer and vinyl ether/maleic acid copolymer at compounding amounts as shown in Table 10 were dissolved in 300g. of a mixture of alcohol and dimethyl formamide of the same amount as that of alcohol- Said solution was applied to an opaque tracing paper and dried in hot air at 90 100C (thickness of film after drying: 2 microns).

Table I Treatment N-Vinyl Vinyl ether/maleic acid No. pyrrolidone copolymer g.)

polymer (g) PVPK-90 Methyl vinyl ether/maleic acid 1 l g.) mono-n-octyl ester copolymer [Vlll] (15 g.) PVPK-90 Methyl vinyl ether/maleic acid 2 12 g.) mono-n-octadceyl ester copolymer l l g-) PVP/VAE- n-butyl vinyl ether/maleic acid 3 735* mono amide copolymer (1 g) [X1 g) PVPK-90 n-butyl vinyl ether/malcic acid 4 (14 g.) mono-N-l-propyl amide compolymer [XII] (15 g.) PVPK-90 Methyl vinyl ether/maleic acid 5 12 g.) mono N-methyl-N-octadecyl amide copolymer [XV] 15 g.) PVP/VAE- n-butyl vinyl ethcr/maleic acid 6 535** mono N-methyl amide copolymer (l5g.) lXl] (l5g.)

Note:

*PVP/VAE-735: N-vinyl pyrrolidonc/vinyl acetate 70/30 copolymer (G A F co) *PVP/VAE-535: N-vinyl pyrrolidone/vinyl acetate 50/50 copolymer ((i A F co) (g.: weight of solid content) The sheet thus produced was cut to form a tape and was permitted to stand at room temperature for 10 days. Said tape was charged into an oscillograph of an electrocardiograph, was traced by a heated stylus (head temperature: 120C) and then developed by moistening the surface of film by a felt impregnating a dye liquid developer to obtain the following results.

Treatment Dye Devellmage Back No. liquid oping density ground Remarks developer time density (seconds) I l D-l 3 middle 0.02 D-Vl 3 large 0.03 2 D-l 3 small 0.01 D-Vll 3 large 0.02 3 D-l 3 middle 0.02 line is D-Vll 3 large 0. l blurred 4 D-l 3 small 00] D-Vl 3 large 0.04 5 D-Vll 5 large 0.02 6 D-Vlll 5 large 0.03

Note: Composition of dye liquid developer D-Vl Anthraquinone Blue AB 0.3 g. Alcohol 30 ml. Water 70 ml. D-Vll Anthraquinone Blue AB 0.3 g. Alcohol 70 ml. Water 30 ml. D-Vlll Anthraquinone Blue AB 0.3 g. i-propyl alcohol 50 ml. Water 50 ml.

EXAMPLE 4 polymer [Vll] were dissolved in 300g. of a mixture of alcohol and dimethyl formaldehyde l l The resulting solution was applied vto a polyester sheet at the thickness of about 3 microns (after drying) and dried to obtain a master. The master after standing for 10 days at room temperature can be used stably. The master was cut in the dimension of a cabinet and a small hole was provided in said master for registration.

On the other hand, black-white originals corresponding to each of three colors for regeneration of said three colors were prepared, and each original was passed through a Thermofax copying machine with said master for exposure. The master was developed by the following liquid developer corresponding to each color, and lightly washed with water to obtain masters of cyan, magenta and yellow.

Composition of Cyan liquid developer:

D-lX Anthraquinone Blue AB l.] g.

Sodium primary phosphate- 10 g. monohydrate v Water l000 ml.

Composition of Magenta liquid developer:

D-X Anthraquinone lupinol R conc 4.0 g.

Sodium primary phosphate-mono 13 g. hydrate Borax L0 g. Water 1000 ml.

Yellow liquid developer:

D-Xl Tartrazine 2.0 g.

Sodium primary phosphate- 20 g. monohydrate Borax l0 g. Water I000 ml.

A baryta paper coated with gelatine was mordanted as follows:

Solution No. l: Aluminium sulfate 100 g.

Water 500 ml.

Solution No.2: Sodium carbonate 20 g.

Water 250 ml.

This exmaple shows that the thermal recording sheet A baryta paper was dipped in the mordanting solution produced by adding solution No.2 to solution No.1 for 5 minutes, then dipped in 5% solution of sodium acetate for 5 minutes, and washed with water for 5 minutes.

The coloring matters were transferred to said baryta paper by laying one color master upon the others in predetermined positions respectively on said baryta paper and squeezing to obtain color prints of cyan, 'magenta and yellow.

Said master may be used repeatedly at least 20 times. The black-white original for printing of a master may be produced easily by a known method. For example the black-white intermediate original for regenerating yellow, magenta and cyan may be obtained by laying each filter of blue green and red on a colored original respectively and copying by an electrophotographic copying machinev on a panchromatically-sensitized ZriO electrophotographic paper. Since the toner developer used for electrophotographic copying paper absorbs effectively the light from the light souce of a Thermofax copying machine, the intermediate original thus obtained may be utilized to produce a master.

7 29 30 Colouring matters except the described above which Table l l -Cntinued are suitable for development and transferring are as fol- Sumpl Ester radicals of methyl Developing Buck lOWSZ No. vinyl ester/maleic acid ground 1. Cyans: v mono ester copolymer Speed density Patent Blue c n 5 Z-cthylhexyl low low B illi Bl 6 n-decyl low low Alizarme Blue (AB) 7 mlddk 0w Fast And Green B I I "(iantrcz ESE-Z25 (manufactured by (iAF) Mlgentds' i r *Gantrez PIS-3354 (manufactured by ()AF) Acid Magenta 28 cone. ""(ianlrez F5425 (manufactured by GAF) Fast Fuchsine Fast Crimson 6 BL Violamine RR EXAMPLE 6 Yellow! l5g. of poly-N-vinyl-S-methyl-2-oxazolidone (K Qumorme YellQw value is 32; lognrel [7.5Ko l+l .5Ko)] K0, Pontflmme Yellow CH (C K=l ()Ko, 1 rel. is specific viscosity) and 30g. of methyl Pontamlne ast yellow NN vinyl ether/maleic acid mono-n-butyl ester (trade namezGantrez ES-425) were dissolved in300g. of di- EXAMPLE 5 methyl formaldehyde. Said solution was applied to .a polyester film subjected to a treatment imparting hy- K 195g. of poly fN-v1nyl pyrrollldone (trdjie dt PVP drophilic property at the thickness of 2.5 microns 15% ether/m4 jj' (after drying) and dried at 80C. After 7 days, said film Copolymer f vdnous lengths o ester l was laid on an original and printed by a Thermalfax chains were combined to produce a thermal recording Copying machine and immediately developed in the dye Sheet by the Same procedure that of Example liquid developer D] for 5 seconds to obtain about I .3 pussefl ,through a Thermoflex Copying maof maximum density (red filter was used) and 0.03 of ch ne with an original and developed by the dye develbackground density Furthermore, 18g of opmg soluuor} Table l I sh ows that the longer the methyl-2-oxazolidone/vinyl acetate copolymer (mixing length of chain of the alkyl radical, the longer the deratio 50/50) was used in place of -5 Velopmg tlme that. the Y S Speed de creases' yl-2-oxazolidone to produce the same thermal recordwhen the devcloplrlg Speed too a mpld f ing sheet. Said thermal recording sheet was developed mem may be posslble but the background denslty by the dye liquid developer D-Vll disclosed in Example tends to Increase if the developing time and tempera- 3 to obtain the Same Clear image as that i E l 3 ture are not controlled When the alkyl chain is not less than C the developing speed is low, but an image hav- EXAMPLE 7 ing a continuous tone and a Clear background is Solutions of various compounds were prepared, and tamed. It is preferred to add an organic solvent miscible two Solutions Selected therefrom were i d i h h with water such as alcohol, acetone; methyl ethyl keother for a gel time test. tone, dioxane and the like to a dye liquid developer to A mixture f two Compounds i h Same amount was increase the image y- 40 dissolved in a suitable solvent for coating, and said solution was applied to a polyester film at the thickness of a Table l l 2 4 microns (after drying) .and' dried to prepare a sam- Samplc Ester radicals of methyl Developing Back P The heat n ty tested wlth'respectto S'ald No. vinyl cster/maleic acid ground l The heat sens t v ty was deten'mned by udgmg "lmlymcr Spccd dens'ty whether an image havingcontrast was formed or not 1 Methyl y g g when said sample was pressed by a heat wedge and de- 2 Methyl" high high 3 p py (2l high middle veloped by r1 dye liquid developer. The results are 4 n-butyl" middle lOW shown in Table I2.

Table 12 Expcri- Solvent Homoge- Heat ment Gela for neity of Sensi- Nor Compound (A) Compound (B) Solvent tion Coating layer tivity Remarks 1 PVP K-JO Vinyl acetate] alcohol alcohol a little maleic acid mono DMF l/l) opaque ethyl ester copolymer l/l 2 Styrenc/malcic alcohol alcohol} opaque acid mono ethyl DMF (1/1 ester copolymer 1/1) 3 Polystyrene chlorochloroopaque Phase l'orm form separate 4 Polyvinyl water water trans alcohol parent 5 Polymcthyl water water transvinyl ether parent 6 Polyvinyl alcohol DMF Phase hydrogen separate phthalate 7 Cellulose alcohol DMF a little Phase r hydrogen opaque separate phthalatc Table lZ-continued Experiv Solvent Homoge- Heat ment (ielafor ncity ol'-- Sensi- No, Compound (A) Compound (8) Sohcnt' tion Coating layer tivity Remarks 8 Methyl cellulose alcohol DMF transhydrogen parent succinate 9 Bcnzyl cellulose alcohol DMF transhydrogen parent succinate ll) P-sulfohenzene water DMF a little cellulose acetate opaque I l Ethyl cellulose alcohol alcohol transparent I 2 Ethyl/hydrosy alcohol alcohol trans- -llethyl cellulose DMF l/l parent l3 Mono ammonium alcohol alcohol/ trans Back salt of methyl DMF l/l parent -ll- Ground vinyl ether/ density: 1 maleic acid a little copolymer high l4 N-vinyl Mono-N-methyl alcohol alcohol/ trans- -H- pirrolidonc/ ammonium salt of DMF l/ l parent vinyl acetate methyl vinyl copolymer cther/maleic acid 70/30 copolymer l5 Hydroxy ethyl alcohol l a little cellulose opaque l6 Poly-N-vinyl Methyl vinyl alcohol transllpiperidone cther/maleic parent a acid mono ethyl ester l i l7 Poly-N-vinyl alcohol v -llcaprolactam I I8 Poly-N-vinyl i alcohol i -H- morpholinone l9 Poly-N-vinylalcohol/ H- l 2-Oxazolidone water i l/ l 2O Poly-N- 7 vinyl imidazole 1 I i 2 l Poly-4- alcohol vinyl pyridine 22 Poly-N-vinyl- Hydroxy ethyl S-methyl-Z- cellulose oxazolidone 23 Methyl vinyl H- ether/maleic acid mono-N- i-propyl amide r 24 N-vinyl-S- -H- mcthyl-2- oxazolidone/ vinyl acetate copolymer ('l/l 25 Polyvinyl alcohol methyl ether 26 Polyvinyl Polyvinyl methyl v 4 methyl ether ether V r 27 Polyvinyl Methyl vinyl acetate ether/maleic acid mono ethyl ester 7 28 Polyethylene Resol type phenol MEK oxide formaldehyde resin 29 PVP K-90 Succinic acid alcohol alcohol monobennzyl ester 30 N-octyl methyl vinyl ether/ alcohol pyrrolidone malcic acid monobutyl ester 31 N-vinyl pyrrolidone/metacrylic acid/ DMF methyl methacrylate eopolymer l:l:l

Solvent for testing'of gelation Note:

Gelation: No gelation: The higher a contrast of an image is, the more number of+ is.

EXAMPLE 8 upon a pure rose image. Furthermore, said film recovered, and then was developed in the developing solu- The thermal recording sheet composed of the mixf A O t f v I ture of PVP K-90 and Gantrez ES-425 1 1 as pre- 9 Orange mdge the above mentioned two images.

pared in Example l was developed in a liquid developer of p-rose aniline h drochloride to obtain a ure'rose colored image. Afte r said film stood for about l 24 hours, EXAMPLE 9 an original picture different from the first original pic- This example relates to a method for preparing and ture was printed onto said film and then said printed for using the thermal recording sheet suitable for refilm was developed in the liquid developer of Crystal generating the negative-positive image.

Violet disclosed in Example 1 to form a violet image lOg. of poly-N-vinyl pyrrolidone (trade name: PVP

K-90) was dissolved in 100 ml. of water, and 15 ml. of a 1071 aqueous solution of silver nitrate and a aqueous solution of common salt were added by a Double.

jet method with vigorous stirring. After stirring for 30 minutes, 5g. of hydroquinone, 20g. of sodium sulfite and g. of sodium carbonate were dissolved in 100 ml. of water and 50 ml. of the solution thus obtained was added little by little and stirred for one hour at 40C. The above mentioned procedure was conducted in a light room.

After lowering from 40C to room temperature, the pH was lowered to 4.0- 5.0 with 10% HNO,-; and there was added immediately a solution of 30g. (solid content: 5071) of vinyl methyl ether/maleic acid mono ethyl ester copolymer (trade name: Gantrez ES-425 manufactured by GAF Co) in 100 ml. of alcohol. The.

gel thus formed was separated, washed with water and I then washed with alcohol.

Said gel was dissolved in a mixture of alcohol and dimethyl formamide l 1 and 10g. (solid content: 5g.) of N-vinyl pyridine/vinyl acetate copolymer (trade name: PVP/VAE-735) was added. The resulting solution was applied to a polyester sheet at the thickness of 3 microns (after drying) and dried. The resulting film contained silver colloid and was light brown and had infrared absorbing properties. After stabilizing by standing at room temperature, said sheet was contacted with a negative photography image and exposed to a Xenon flashing discharge lamp (trade mark: Press-150 manufactured by Minicham) at a short distance and immediately developed in the dye liquid developer D-ll to obtain a clear positive image. Said sheet was printed by a step wedge having 2 step and was developed. The maximum density was 1.5 (green filter) and the back ground density was 0.25. Eight steps are observed between the maximum density and the background density.

Said thermal recording sheet may be used for recording by laser scanning. When the laser ray (having a wave length of 6328 A, spot diameter of 2 microns on the sheet and an intensity of 10 milliwatt) scans the thermal recording sheet at 2 m./sec. and said thermal recording sheet was developed with the dye liquid developer D-ll, the record of sharp locus was obtained.

It is effective to use various infrared absorbers such phenyl fluorene derivative. Manganese complex of azo dyes or commercially organic infrared absorbers containing antimony may be used in place of silver coloid in the thermal recording layer.

EXAMPLE 10 This example relates to the effect of an agent used to control the properties of the image.

1. When PVP/ES-425 is 6/4 (molar ratio) A solution of 12g. of poly-N-vinyl pyrrolidone (trade name: PVP K-90, manufactured by GAF), 16g. of methyl vinyl ether/maleic acid mono-n-butyl ester copolymer (50% solution) (trade name: Gantrez ES-425, manufactured by GAF), 150g. of ethanol, 50g. of dimethyl formamide and 10g. of an additive ,was applied to a polyester film, dried and allowed to stand for 10 days at room temperature. The prepared thermal recording sheet was passed through a Thermofax copying machine with an original and developed by a machine under the following condition.

Developing solution: 10% water solution on Malachite Green oxalate.

Developing time: 3 sec. Developing temperature: 30C The results are shown in Table l 3.

D,D,,: lmagc Density-Background Density 2. When PVP/ES-425 is 4/6 (molar ratio) A solution comprised of 8.0g. of poly-N-vinyl pyrrolidone (trade name: PVP K- manufactured by GAF Co), 24g. of methyl vinyl ether/maleic acid mono-nbutyl ester copolymer (50% solution) (trade name: Gantrez ES-425 manufactured by GAF Co), g. of ethanol, 50g. of dimethylformaldehyde and 10g. of an addition agent was applied on a polyester film and dried. After standing for 7 days at room temperature. said thermal recording sheet was passed through a Tharmafax copying machine with a manuscript and developed by machine under the following conditions.

Developing solution: 1.0% water solution of Malachite Green oxalate Developing time: 10 sec.

Developing temperature: 30C The results are shown in Table 14 below.

D,-1),,: Image Density-Background Density Developing by the machine disclosed above is the developing method using the following developing machine. The developing is conducted in such a way that a film transferred by a field roller provides aberration of position to an actuator, a photoswitch connects by said aberration of position, said film is put between crip plates connecting to the comfollower on the film conveyer to be fixed, said film is treated by fountain development, and excess liquid developer scraped off with a blade.

Tables 13 and 14 show that the most effective additive is 9-fluorene carboxylic acid in 1 and benzophenone in (2). The results show that weak mutual action among high polymer (A), high polymer (B) and the additive provides an influence on the image property.

EXAMPLE 11 15g. of polyvinyl pyrrolidone (trade name: PVP K-90, manufactured by GAF)'was dissolved in 150 g. of alcohol and g. of methyl vinyl ether/maleic acid mono-n-butyl ester copolymer(trade name: Gantrez ES-425, manufactured by GAF) (solid content: was added to. said solution and permitted to stand to obtain a gel-like high polymer complex. 150g. of dimethyl formamide was added to said gel-like Complex to obtain a homogeneous and clear solution. Said solution was applied to a polyester film at a thickness of microns (the film having been subjected to a treatment imparting a hydrophilic property) dried by hot air'at 70: C. (The thickness of said film was 2 microns after drying). After standing for several days at room temperature (about 20C), the properties of said sheet such heat sensitive temperature, contrast and the like are stabilized. Said thermal recording sheet is EXAMPLE 12 When a latent image formed on a thermal recording sheet prepared by the methodof Example ll except adding a small amount of phenolphthalein to the composition of Example 1 l was exposed to ammonia vapor for 10 minutes, a reddish rose color was formed at the portion of the latent image. Thus a visible image was obtained.

EXAMPLE I 3 Silver behenate (25g) and hydroquinone lg.) were added to and dispersed in a solution of theco mplex obtained in Example I in dimethylformamide, coated on a polyester film of 70 microns in thickness and dried at room temperature. The resulting thermal recording sheet was contacted with a first original and passed through a copier which was adjusted to give a thermal pattern of C. to produce a dark brown image due to the reduction of the silver behenate. Then a portion of the thermal recording member having no image was contacted with a second original and passed through a copier adjusted to give a thermal pattern of 60-80. The silver behenate did not react with the complex under such temperature conditions and failed to produce any image of the second original.

The resulting sheet was developed with the dye liquid developer D-l in Example I and there was obtained an image of the second original.

We claim:

1. A thermal recording member useful for forming a reversible latent image by heating which is capable of being developed into a permanent visible image, said recording member comprising a support having thereon a uniform and transparent recording layer composed of a heat-sensitive composition which comprises a polymer complex including a polymer moiety which is normally dyeable at room temperature but which, in the polymer complex, is dyeable only after heating the complex to an elevated temperature.

wherein said polymer complex is acomplex of a polymer (A) and a polymer (B); and wherein said polymer (A) isa dyeable polymer selected from the group consisting of homopolymers and copolymers of N-vinyl lactams, N-vinylcyclic carbamates, N-vinyl imidazoles, vinyl pyridines, alkylene oxides and acrylamides; and

wherein said polymer (B) is selected from the group consisting of polymers having a carboxylic acid radical, a sulfonic acid radical or an OH radical.

2. A thermal recording member according to claim 1 wherein said polymer (A) is a homopolymer of one of said group, a copolymer of morethan one of said group or, a copolymer of one of said group with a different vinyl monomer. Y i

3. A thermal recording member according to claim 2 wherein said different vinyl monomer is selected from the group consistingof methacrylates, acrylates. acrylamides, acrylonitrile. vinyl ethers, vinyl acetate, vinyl imidazoles and ethylene. I

4. A thermal recording member accroding to claim I v mercaptobenzothiazole, N-vinyl imidazole, N-vinyl-ZZ- methyl imidazole, N-vinyl-4-methyl imidazole, ethylene oxide, propylene oxide, methacrylamide, acrylamide, N-methyl acrylamide, N-n-butyl acrylamide, N-

benzyl acrylamide, 2-vinylpyridine and ,4-vinyl, pyridine.

5. A thermal recording member according to claim 1 in which said polymer ('8) is selected from the group consisting of polyesters obtained by reacting an aliphatic polyhydric carboxylic acid and diols, acid'cellulose derivatives, an acid polyvinyl polymer, an acrylic acid polymer, a methacrylic'acid polymer, an a, [3- unsaturated acid polymer, acid polyvinyl alcohol derivatives, cellulose ethers, a phenolic'resin, a cresol-formaldehyde resin and a phenoxyacetici acidformaldehyde resin. 7 6. A thermal recording member according to claim-l, in which said polymer (B) is selected from the group consisting of homopolymers and copolymers of maleic anhydride, maleic anhydride mono-esters and maleic anhydride mono-amides. Y

7. A thermal recording member according to claim in which said polymer (B) is selected from the group consisting of copolymers of l) and a, B-unsaturated acid selected from the group consisting of maleic anhydride, maleic anhydride mon-esters, maleic anhydride mono-amides, itaconic anhydride, citraconic anhydride and diester fumarate, and (2) a vinyl monomer selected from the group consisting of vinyl acetate, vinyl ethers,

, acrylamide, vinyl esters, ethylene and acrylic esters.

8. A thermal recording member according-to claim 1 in whichsaid'polymer (B) is selected from the group consisting of methyl vinyl ether/maleic acid copolymers, methyl vinyl ether/maleic acid mono n-butyl ester copolymers, methyl vinyl ether/maleic acid mono-N-n-hexylamide copolymers, methyl vinyl ether/maleic acid mono-n-octyl ester copolymers,

N-vinyl-5-methyl-2-oxazolidone, I N- 3 I' 

1. A THERMAL RECORDING MEMBER USEFUL FOR FORMING A REVERSIBLE LATENT IMAGE BY HEATING WHICH IS CAPABLE, OF BEING DEVELOPED INTO A PERMANENT VISIBLE IMAGE, SAID RECORDING MEMBER, COMPRISING A SUPPORT HAVING THEREON A UNIFORM AND TRANSPARENT RECORDING LAYER COMPOSED OF A HEAT-SENSITIVE COMPOSITION WHICH COMPRISES A POLYMER COMPLEX INCLUDING A POLYMER MOIETY WHICH IS NORMALLY DYEABLE AT ROOM TEMPERATURE BUT WHICH, IN THE POLYMER COMPLEX, IS DYEABLE ONLY AFTER HEATING THE COMPLEX TO AN ELEVATED TEMPERATURE, WHEREIN SAID POLYMER COMPLEX IS A COMPLEX OF A POLYMER (A) AND A POLYMER (B), AND WHEREIN SAID POLYMER (A) IS A DYEABLE POLYMER SELECTED FROM THE GROUP CONSISTING OF HOMOPOLYMERS AND COPOLYMERS
 2. A thermal recording member according to claim 1 wherein said polymer (A) is a homopolymer of one of said group, a copolymer of more than one of said group or a copolymer of one of said group with a different vinyl monomer.
 3. A thermal recording member according to claim 2 wherein said different vinyl monomer is selected from the group consisting of methacrylates, acrylates, acrylamides, acrylonitrile, vinyl ethers, vinyl acetate, vinyl imidazoles and ethylene.
 4. A thermal recording member accroding to claim 1 in which said polymer (A) is selected from the group consisting of homopolymers and copolymers of N-vinyl pyrrolidone, N-vinyl-3-methyl pyrrolidone, N-vinyl-5-methyl pyrrolidone, N-vinyl-3,3,5-trimethyl pyrrolidone, N-vinyl-3-benzylpyrrolidone, N-vinyl piperidone, N-vinyl-4-methyl piperidone, N-vinyl caprolactam, N-vinyl capryllactam, N-vinyl-3-morpholinone, N-vinyl thiopyrrolidone, N-vinyl-2 pyriodone, N-vinyl-2-oxazolidone, N-vinyl-5-methyl-2-oxazolidone, N-vinyl-5-ethyl-2-oxazolidone, N-vinyl-4-methyl-2-oxazolidone, N-vinyl-2-thio-oxazolidone, N-vinyl-2-mercaptobenzothiazole, N-vinyl imidazole, N-vinyl-2-methyl imidazole, N-vinyl-4-methyl imidazole, ethylene oxide, propylene oxide, methacrylamide, acrylamide, N-methyl acrylamide, N-n-butyl acrylamide, N-benzyl acrylamide, 2-vinylpyridine and 4-vinyl pyridine.
 5. A thermal recording member according to claim 1 in which said polymer (B) is selected from the group consisting of polyesters obtained by reacting an aliphatic polyhydric carboxylic acid and diols, acid cellulose derivatives, an acid polyvinyl polymer, an acrylic acid polymer, a methacrylic acid polymer, an Alpha , Beta -unsaturated acid polymer, acid polyvinyl alcohol derivatives, cellulose ethers, a phenolic resin, a cresol-formaldehyde resin and a phenoxyacetic acidformaldehyde resin.
 6. A thermal recording member according to claim 1, in which said polymer (B) is selected from the group consisting of homopolymers and copolymers of maleic anhydride, maleic anhydride mono-esters and maleic anhydride mono-amides.
 7. A thermal recording member according to claim 1 in which said polymer (B) is selected from the group consisting of copolymers of (1) and Alpha , Beta -unsaturated acid selected from the group consisting of maleic anhydride, maleic anhydride mon-esters, maleic anhydride mono-amides, itaconic anhydride, citraconic anhydride and diester fumarate, and (2) a vinyl monomer selected from the group consisting of vinyl acetate, vinyl ethers, acrylamide, vinyl esters, ethylene and acrylic esters.
 8. A thermal recording member according to claim 1 in which said polymer (B) is selected from the group consisting of methyl vinyl ether/maleic acid copolymers, methyl vinyl ether/maleic acid mono n-butyl ester copolymers, methyl vinyl ether/maleic acid mono-N-n-hexylamide copolymers, methyl vinyl ether/maleic acid mono-n-octyl ester copolymers, methyl vinyl ether/maleic acid mono-n-octadecyl ester copolymers, n-butyl vinyl ether/maleic acid mono-amide copolymers, n-butyl vinyl ether/maleic acid mono-N-i-propyl amide copolymers, methyl vinyl ether/maleic acid mono-N-methyl-N-octadecyl amide copolymers, n-butyl vinyl ether/maleic acid mono-N-methyl amide copolymers, n-butyl ether/maleic acid mono ethyl ester copolymers, vinyl acetate/maleic acid mon-ethyl ester copolymers, methyl cellulose hydrogen succinate, benzyl cellulose hydrogen succinate, p-sulfobenzene cellulose acetatE, ethyl hydroxyethyl cellulose, mono-ammonium salts of methyl vinyl ether/maleic acid copolymers, mono-N-methyl ammonium salts of methyl vinyl ether/maleic acid copolymers, hydroxyethyl cellulose, resol-type phenol formaldehyde resins and succinic acid monobenzyl esters.
 9. A thermal recording member according to claim 1 in which the heat-sensitive composition further contains a proton acceptor or a proton donor.
 10. A thermal recording member according to claim 9, in which the proton acceptor is selected from the group consisting of:
 11. A thermal recording member according to claim 9 in which the proton donor is selected from the group consisting of FH, HCl, R-COOH, C6H5OH, C6H5NHCOCH3, RCONHR'', C2H5NHC2H5, RCONH2, H2O, Cl3CH, C6H5-NH-C6H5, (CH2)2NH, C6H5NH2 and C6H5CH2NH2, wherein R and R'' are each alkyl or aryl.
 12. A thermal recording member according to claim 1 in which the heat-sensitive composition further contains an aliphatic or aromatic ketone which is non-volatile at room temperature.
 13. A thermal recording member according to claim 1 in which the heat-sensitive composition further contains a member selected from the group consisting of Alpha -chloroanthraquinone, benzophenone, p-dimethyl-aminobenzaldehyde, 9-fluorene carboxylic acid, p-nitro phenol, Michler''s ketone, p-nitro phenyl acetate, p-benzoquinone, benzhydrol and benzoin.
 14. A thermal recording member useful for forming a reversible latent image by heating which is capable of being developed into a permanent visible image, said recording member having a uniform and transparent heat-sensitive recording layer which comprises a polymer complex of a polymer (A) and a polymer (B); wherein said polymer (A) is selected from the group consisting of poly-N-vinyl pyrrolidone, N-vinyl pyrrolidone/vinyl acetate copolymers, poly-N-vinyl-5-methyl-2-oxazolidone, N-vinyl-5-methyl-2-oxazolidone/vinyl acetate copolymers, poly-N-vinyl piperidone, poly-N-vinyl caprolactam, poly-N-vinyl morpholinone, poly-N-vinyl-2-oxazolidone, polyn-N-vinyl imidazole, poly-4-vinyl pyridine, polyethylene oxide and poly-N-octyl pyrrolidone, and wherein said polymer (B) is selected from the group consisting of methyl vinyl ether/maleic acid copolymers, methyl vinyl ether/maleic acid mono-n-butyl ester copolymers, methyl vinyl ether/maleic acid mono-N-n-hexylamide copolymers, methyl vinyl ether/maleic acid mono-n-octyl ester copolymers, methyl vinyl ether/maleic acid mono-n-octadecyl ester copolymers, n-butyl vinyl ether/maleic acid mono-amide copolymers, n-butyl vinyl ether/maleic acid mono-N-i-propyl amide copolymers, methyl vinyl ether/maleic acid mono-N-methyl-N-octadecyl amide copolymers, n-butyl vinyl ether/maleic acid mono-N-methyl amide copolymers, n-butyl vinyl ether/maleic acid mono ethyl ester copolymers, vinyl acetate/maleic acid mono ethyl ester copolymers, methyl cellulose hydrogen succinate, benzyl cellulose hydrogen succinate, p-sulfobenzene cellulose acetate, ethyl hydroxy ethyl cellulose, mono-ammonium salts of methyl vinyl ether/maleic acid copolymers, mono-N-methyl ammonium salts of methyl vinyl ether/maleic acid copolymers, hydroxy ethyl cellulose, resol-type phenol formaldehyde resins and succinic acid monobenzyl ester.
 15. A thermal recording member useful foR forming a reversible latent image by heating which is capable of being developed into a permanent visible image, said recording member having a uniform heat-sensitive recording layer which comprises a polymer complex of poly-N-vinyl pyrrolidone and a methyl vinyl ether/maleic acid mono-n-butyl ester copolymer.
 16. A thermal recording method which comprises forming a reversible latent image by applying a thermal pattern to a recording member having a uniform and transparent heat-sensitive layer which contains a polymer complex of a polymer (A) and a polymer (B), said polymer (A) being selected from the group consisting of homopolymers and copolymers of N-vinyl lactams, N-vinyl cyclic carbamates, N-vinyl imidazoles, vinyl pyridines, alkylene oxides and acrylamides, and said polymer (B) being selected from the group consisting of polymers having a carboxylic acid radical, a sulfonic acid radical or an OH radical, and then contacting said heat-sensitive layer with a dye solution to convert said reversible latent image into a permanent visible image.
 17. A thermal recording method according to claim 16 in which said dye solution is an aqueous dye solution.
 18. A thermal recording method according to claim 16 in which said dye is selected from the group consisting of triphenylmethane dyes, xanthene dyes, mono azo dyes, anthraquinone dyes and ketoimine type dyes.
 19. A thermal recording method according to claim 16 in which said polymer (A) is selected from the group consisting of homopolymers and copolymers of N-vinyl pyrrolidone, N-vinyl-3-methyl pyrrolidone, N-vinyl-5-methyl pyrrolidone, N-vinyl-3,3,5-trimethyl pyrrolidone, N-vinyl-3-benzyl-pyrrolidone, N-vinyl piperidone, N-vinyl-4-methyl piperidone, N-vinyl caprolactam, N-vinyl capryllactam, N-vinyl-3-morpholinone, N-vinyl thiopyrrolidone, N-vinyl-2-pyridone, N-vinyl-2-oxazolidone, N-vinyl-5-methyl-2-oxazolidone, N-vinyl-5-ethyl-2-oxazolidone, N-vinyl-4-methyl-2-oxazolidone, N-vinyl-2-thiooxazolidone, N-vinyl-2-mercaptobenzothiazole, N-vinyl imidazole, N-vinyl-2-methyl imidazole, N-vinyl-4-methyl imidazole, ethylene oxide, propylene oxide, methacrylamide, acrylamide, N-methyl acrylamide, N-n-butyl acrylamide, N-benzyl acrylamide, 2-vinylpyridone and 4-vinyl pyridine.
 20. A thermal recording method according to claim 16 in which said polymer (B) is selected from the group consisting of homopolymers and copolymers of maleic anhydride, maleic anhydride mono-esters and maleic anhydride mono-amides.
 21. A thermal recording method according to claim 16 in which said polymer (B) is selected from the group consisting of copolymers of (1) an Alpha , Beta -unsaturated acid selected from the group consisting of maleic anhydride, maleic anhydride mono-esters, maleic anhydride mono-amides, itaconic anhydride, citraconic anhydride and diester fumarate, and (2) a vinyl monomer selected from the group consisting of vinyl acetate, vinyl ethers, acrylamide, vinyl esters, ethylene and acrylic esters.
 22. A thermal recording method according to claim 16 in which said polymer (B) is selected from the group consisting of methyl vinyl ether/maleic acid copolymers, methyl vinyl ether/maleic acid mono-n-butyl ester copolymers, methyl vinyl ether/maleic acid mono-N-n-hexylamide copolymers, methyl vinyl ether/maleic acid mono-n-octyl ester copolymers, methyl vinyl ether/maleic acid mono-n-octadecyl ester copolymers, n-butyl vinyl ether/maleic acid mon-amide copolymers, n-butyl vinyl ether/maleic acid mono-N-i-propyl amide copolymers, methyl vinyl ether/maleic acid mono-N-methyl-N-octadecyl amide copolymers, n-butyl vinyl ether/maleic acid mono-N-methyl amide copolymers, n-butyl vinyl ether/maleic acid mono ethyl ester copolymers, vinyl acetate/maleic acid mono ethyl ester copolymers, methyl cellulose hydrogen succinate, benzyl ceLlulose hydrogen succinate, p-sulfobenzene cellulose acetate, ethyl hydroxy ethyl cellulose, mono-ammonium salts of methyl vinyl ether/maleic acid copolymers, mono-N-methyl ammonium salts of methyl vinyl ether/maleic acid copolymers, hydroxy ethyl cellulose, resol-type phenol formaldehyde resins and succinic acid monobenzyl ester.
 23. A Thermal recording method which comprises applying a thermal pattern to a recording member having a uniform and transparent heat-sensitive layer which contains a polymer complex of poly-N-vinyl pyrrolidone and a vinyl ether/maleic acid mono ester copolymer. 